Recovery of State Information of a First Tunnel End-Point

1. A method comprising: detecting a crash of a first tunnel endpoint with a backup tunnel endpoint of the first tunnel endpoint; sending a hello message to a second tunnel endpoint from the backup tunnel endpoint, wherein state variables in the hello message are set as current first and second state variables of the backup tunnel endpoint; receiving a response message from the second tunnel endpoint, wherein state variables in the response message comprise first and second state variables of the second tunnel endpoint; setting the second state variable of the backup tunnel endpoint as the first state variable in the response message incremented by one; recovering the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the backup tunnel endpoint incremented by one; initiating a new session between the backup tunnel endpoint and the second tunnel endpoint; sending a session initiation request message from the backup tunnel endpoint to the second tunnel endpoint, wherein state variables in the session initiation request message are set as current first and second state variables of the backup tunnel endpoint; receiving a session initiation response message from the second tunnel endpoint, wherein the state variables in the session initiation response message comprise the first and second state variables of the second tunnel endpoint; recovering the second state variable of the first tunnel endpoint from the first state variable of the second tunnel endpoint present in the session initiation response message; and disconnecting the initiated session, wherein the first state variable comprises a sequence number for sent messages and the second state variable comprises a sequence number for received messages.

2. The method according to claim 1 , wherein when the second state variable of the second tunnel endpoint in the response message does not equal the first state variable of the backup tunnel endpoint incremented by one, the method further comprises: setting the first state variable of the backup tunnel endpoint as the second state variable in the response message; sending a hello message to the second tunnel endpoint from the backup tunnel endpoint, wherein the state variables in the hello message are set as current first and second state variables of the backup tunnel endpoint; receiving a response message from the second tunnel endpoint, wherein the state variables in the response message comprise the first and second state variables of the second tunnel endpoint; setting the second state variable of the backup tunnel endpoint as the first state variable in the response message incremented by one; and recovering the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the backup tunnel endpoint incremented by one.

3. The method according to claim 1 , wherein the first state variable comprises the sequence number of a last sent message and the second state variable comprises a next sequence number expected to receive.

4. The method according to claim 1 , wherein the point to point connection is a Layer Two Tunneling Protocol tunnel.

5. An apparatus, comprising: a detector configured to detect a crash of a first tunnel endpoint, a transmitter configured to send a hello message to a second tunnel endpoint, wherein state variables in the hello message are set as current first and second state variables of the apparatus, a receiver configured to receive a response message from the second tunnel endpoint, wherein state variables in the response message comprise first and second state variables of the second tunnel endpoint, a recovering entity configured to set the second state variable of the apparatus as the first state variable in the response message incremented by one, wherein the recovering entity is configured to recover the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the apparatus incremented by one, the transmitter is configured to initiate a new session between the apparatus and the second tunnel endpoint by sending a session initiation request message to the second tunnel endpoint, wherein state variables in the session initiation request message are set as current first and second state variables of the apparatus, the receiver is configured to receive a session initiation response message from the second tunnel endpoint, wherein state variables in the session initiation response message comprise the first and second state variables of the second tunnel endpoint, the recovering entity is configured to recover the second state variable of the first tunnel endpoint from the first state variable of the second tunnel endpoint present in the session initiation response message, and the transmitter is configured to disconnect the initiated session by sending a disconnecting message to the second tunnel endpoint, wherein the first state variable comprises a sequence number for sent messages and the second state variable comprises a sequence number for received messages.

6. The apparatus according to claim 5 , wherein when the second state variable of the second tunnel endpoint in the response message does not equal the first state variable of a backup tunnel endpoint incremented by one the recovering entity is configured to set the first state variable of the apparatus as the second state variable in the response message, the transmitter is configured to send a hello message to the second tunnel endpoint, wherein the state variables in the hello message are set as current first and second state variables of the apparatus, the receiver is configured to receive a response message from the second tunnel endpoint, wherein the state variables in the response message comprise first and second state variables of the second tunnel endpoint, the recovering entity is configured to set the second state variable of the apparatus as the first state variable in the response message incremented by one, and the recovering entity is configured to recover the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the apparatus incremented by one.

7. The apparatus according to claim 5 , wherein the transmitter is configured to send an incoming call request message to the second tunnel endpoint as the session initiation request message, and the receiver is configured to receive an incoming call reply message as the session initiation response message.

8. The apparatus according to claim 5 , wherein the transmitter is configured to send an outgoing call request message to the second tunnel endpoint as the session initiation request message, and the receiver is configured to receive an outgoing call reply message as the session initiation response message.

9. The method according to claim 1 , further comprising: sending an incoming call request message to the second tunnel endpoint as the session initiation request message; and receiving an incoming call reply message as the session initiation response message.

10. The method according to claim 1 , further comprising: sending an outgoing call request message to the second tunnel endpoint as the session initiation request message; and receiving an outgoing call reply message as the session initiation response message.

11. The apparatus according to claim 5 , wherein the first state variable comprises the sequence number of a last sent message and the second state variable comprises a next sequence number expected to receive.

12. The apparatus according to claim 5 , wherein the apparatus comprises a Layer Two Tunneling Protocol tunnel endpoint.

13. A system, comprising: a first tunnel endpoint; a backup tunnel endpoint for the first tunnel endpoint; a second tunnel endpoint; a point to point connection between the first tunnel endpoint and the second tunnel endpoint; a first state variable in each of the first and second tunnel endpoints comprising a sequence number for sent messages; and a second state variable in each of the first and second tunnel endpoints comprising a sequence number for received messages, wherein the backup tunnel endpoint comprises a detector configured to detect a crash of the first tunnel endpoint, a transmitter configured to send a hello message to the second tunnel endpoint, wherein state variables in the hello message are set as current first and second state variables of the apparatus, a receiver configured to receive a response message from the second tunnel endpoint, wherein state variables in the response message comprise the first and second state variables of the second tunnel endpoint, a recovering entity confirmed to set the second state variable of the apparatus as the first state variable in the response message incremented by one, wherein the recovering entity is configured to recover the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the apparatus incremented by one, the transmitter is configured to initiate a new session between the apparatus and the second tunnel endpoint by sending a session initiation request message to the second tunnel endpoint, wherein state variables in the session initiation request message are set as current first and second state variables of the apparatus, the receiver is configured to receive a session initiation response message from the second tunnel endpoint, wherein the state variables in the session initiation response message comprise the first and second state variables of the second tunnel endpoint, the recovering entity is configured to recover the second state variable of the first tunnel endpoint from the first state variable of the second tunnel endpoint present in the session initiation response message, and the transmitter is configured to disconnect the initiated session by sending a disconnecting message to the second tunnel endpoint, wherein the first state variable comprises a sequence number for sent messages and the second state variable comprises a sequence number for received messages.

14. The system according to claim 13 , wherein when the second state variable in the response message does not equal the first state variable of the backup tunnel endpoint incremented by one the recovering entity is configured to set the first state variable of the backup tunnel endpoint as the second state variable in the response message, the transmitter is configured to send a hello message to the second tunnel endpoint, wherein the state variables in the hello message are set as current first and second state variables of the backup tunnel endpoint, the receiver is configured to receive a response message from the second tunnel endpoint, wherein the state variables in the response message comprise first and second state variables of the second tunnel endpoint, the recovering entity is configured to set the second state variable of the backup tunnel endpoint as the first state variable in the response message incremented by one; and the recovering entity is configured to recover the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the backup tunnel endpoint incremented by one.

15. The system according to claim 13 , wherein the transmitter is configured to send an incoming call request message to the second tunnel endpoint as the session initiation request message, and the receiver is configured to receive an incoming call reply message as the session initiation response message.

16. The system according to claim 13 , wherein the transmitter is configured to send an Outgoing call Request message to the second tunnel endpoint as the session initiation request message, and the receiver is configured to receive an Outgoing call reply message as the session initiation response message.

17. The system according to claim 13 , wherein the first state variable comprises the sequence number of a last sent message and the second state variable comprises a next sequence number expected to receive.

18. The system according to claim 13 , wherein the tunnel endpoints comprise Layer Two Tunneling Protocol tunnel endpoints.

19. A computer program embodied on a computer readable medium, the computer program being configured to control a data processing device to perform: detecting a crash of a first tunnel endpoint with a backup tunnel endpoint of the first tunnel endpoint; sending a hello message to the second tunnel endpoint from the backup tunnel endpoint, wherein state variables in the hello message are set as current first and second state variables of the backup tunnel endpoint, receiving a response message from the second tunnel endpoint, wherein state variables in the response message comprise first and second state variables of the second tunnel endpoint, setting the second state variable of the backup tunnel endpoint as the first state variable in the response message incremented by one, recovering the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the backup tunnel endpoint incremented by one, initiating a new session between the backup tunnel endpoint and the second tunnel endpoint, sending a session initiation request message from the backup tunnel endpoint to the second tunnel endpoint, wherein state variables in the session initiation request message are set as current first and second state variables of the backup tunnel endpoint, receiving a session initiation response message from the second tunnel endpoint, wherein state variables in the session initiation response message comprise the first and second state variables of the second tunnel endpoint, recovering the second state variable of the first tunnel endpoint from the first state variable of the second tunnel endpoint present in the session initiation response message, and disconnecting the initiated session, wherein the first state variable comprises a sequence number for sent messages and the second state variable comprises a sequence number for received messages.

20. The computer program according to claim 19 , wherein when the second state variable of the second tunnel endpoint in the response message does not equal the first state variable of the backup tunnel endpoint incremented by one, said program is further configured to perform setting the first state variable of the backup tunnel endpoint as the second state variable in the response message; sending a hello message to the second tunnel endpoint from the backup tunnel endpoint, wherein the state variables in the hello message are set as current first and second state variables of the backup tunnel endpoint; receiving a response message from the second tunnel endpoint, wherein the state variables in the response message comprise the first and second state variables of the second tunnel endpoint; setting the second state variable of the backup tunnel endpoint as the first state variable in the response message incremented by one; and recovering the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the backup tunnel endpoint incremented by one.

21. The computer program according to claim 19 , wherein said program further configured to perform: sending an incoming call request message to the second tunnel endpoint as the session initiation request message; and receiving an incoming call reply message as the session initiation response message.

22. The computer program according to claim 19 , wherein said program further configured to perform: sending an outgoing call request message to the second tunnel endpoint as the session initiation request message; and receiving an outgoing call reply message as the session initiation response message.

23. The computer program according to claim 19 , wherein the first state variable comprises the sequence number of a last sent message and the second state variable comprises a next sequence number expected to receive.

24. An apparatus, comprising: detecting means for detecting a crash of a first tunnel endpoint; sending means for sending a hello message to the second tunnel endpoint from the backup tunnel endpoint, wherein state variables in the hello message are set as current first and second state variables of the backup tunnel endpoint, receiving means for receiving a response message from the second tunnel endpoint, wherein state variables in the response message comprise first and second state variables of the second tunnel endpoint, setting means for setting the second state variable of the backup tunnel endpoint as the first state variable in the response message incremented by one, recovering means for recovering the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the backup tunnel endpoint incremented by one, initiating means for initiating a new session between the backup tunnel endpoint and the second tunnel endpoint, wherein the sending means are configured to send a session initiation request message from the backup tunnel endpoint to the second tunnel endpoint, wherein state variables in the session initiation request message are set as current first and second state variables of the backup tunnel endpoint, the receiving means receives a session initiation response message from the second tunnel endpoint, wherein state variables in the session initiation response message comprise the first and second state variables of the second tunnel endpoint, the recovering means recovers the second state variable of the first tunnel endpoint from the first state variable of the second tunnel endpoint present in the session initiation response message, and disconnecting means for disconnecting the initiated session, wherein the first state variable comprises a sequence number for sent messages and the second state variable comprises a sequence number for received messages.

25. A system, comprising: a first tunnel endpoint; a backup tunnel endpoint for the first tunnel endpoint; a second tunnel endpoint; a point to point connection between the first tunnel endpoint and the second tunnel endpoint; a first state variable in each of the first and second tunnel endpoints comprising a sequence number for sent messages; and a second state variable in each of the first and second tunnel endpoints comprising a sequence number for received messages, wherein the backup tunnel endpoint comprises detecting means for detecting a crash of the first tunnel endpoint, sending means for sending a hello message to the second tunnel endpoint from the backup tunnel endpoint, wherein state variables in the hello message are set as current first and second state variables of the backup tunnel endpoint, receiving means for receiving a response message from the second tunnel endpoint, wherein state variables in the response message comprise the first and second state variables of the second tunnel endpoint, setting means for setting the second state variable of the backup tunnel endpoint as the first state variable in the response message incremented by one, recovering means for recovering the first state variable of the first tunnel endpoint when the second state variable in the response message equals the first state variable of the backup tunnel endpoint incremented by one, initiating means for initiating a new session between the backup tunnel endpoint and the second tunnel endpoint, wherein the sending means sends a session initiation request message from the backup tunnel endpoint to the second tunnel endpoint, wherein state variables in the session initiation request message are set as current first and second state variables of the backup tunnel endpoint, the receiving means receives a session initiation response message from the second tunnel endpoint, wherein state variables in the session initiation response message comprise the first and second state variables of the second tunnel endpoint, the recovering means recovers the second state variable of the first tunnel endpoint from the first state variable of the second tunnel endpoint present in the session initiation response message, and disconnecting means for disconnecting the initiated session, wherein the first state variable comprises a sequence number for sent messages and the second state variable comprises a sequence number for received messages.